Sulphurised calcium alkyl phenate detergents are well known additive components for internal combustion engine crankcase lubricating oil compositions. However, alkylphenols used in their manufacture have some undesirable properties, such as giving rise to corrosion. Furthermore, certain alkylphenols (nonylphenol, tetrapropenylphenol) are classified as reproductive toxins.
Various routes are known in the art for manufacturing such phenate detergents and they result in a multi-constituent product that comprises mainly a colloidal system (a calcium carbonate core stabilized by a sulphurised phenate surfactant) with other species in an oil medium. However, the alkylphenol starting materials are not completely consumed in the reaction to produce the final detergent.
Levels of unreacted alkylphenol in the final detergent may, for example, range from 2 to 20% and, at these levels, may constitute a problem for the reasons indicated above. There is therefore a need to reduce these levels, but without introducing performance debits.
The prior art describes ways of solving the problem, but they are generally expensive to carry out. WO 2011066115 describes a method of making phenate using alkylphenols synthesised with alkyl chains derived from isomerized linear olefins. These alkylphenol products are made by alkylation of phenol with a partially-branched olefin that had been prepared from a linear olefin by a generalised isomerization step; their use for the manufacturing of detergents that are substantially free of endocrine disruptive chemicals is described.
Also, a number of references describe the synthesis of alkylphenols to form structures compositionally different from nonylphenol and tetrapropenylphenol, and some references further describe the synthesis of phenates from these materials. U.S. Pat. Nos. 5,318,710, 5,320,762 and 5,320,763 describe Group II metal overbased sulphurised alkylphenol compositions derived from alkylphenols enriched in alkylphenol containing substantially straight chain alkyl chains. WO 2010014829, WO 2011096920, EP 1108704, US 20080269351 and US 20110118160 are all further examples of attempts at producing an alkyl phenol that is structurely different from tetrapropenylphenol and nonylphenol. It is stated in WO 2011096920 that the composition produced will reduce the reprotoxicological activity of the additive, compared with additives based on propylene tetramer.
Additionally, US 20090143264 is an example in the art describing a low tetrapropenylphenol phenate product whilst continuing to use it as the alkylphenol feedstock, stating that HBN Phenates with a residual TPP content of less than 2 mass % have been prepared.